The present invention generally relates to the treatment of cardiac arrhythmias (atrial and ventricular) such as, but not limited to, atrial fibrillation and/or to the treatment of vascular restenosis after the use of other ablation techniques. More specifically, the present invention is directed to unique apparatus and/or methods employing ionizing radiation for ablating cardiac issue to treat cardiac arrhythmias.
The coordinated contraction of the various chambers of the human heart during a normal heartbeat is controlled by a relatively complex electrical system. The electrical signal that initiates each heartbeat begins at an area in the right atrium commonly called the “sinus node” or the “sinoatrial node.” The electrical signal rapidly spreads across the right and left atria. The electrical signal is conducted to the ventricles of the heart through a connection called the atrioventricular node (AV node). From the atrioventricular node, the electrical signal passes along a bundle of special cells in the heart, known as a Bundle of His, which spreads the electrical signal rapidly through the ventricles.
The regular and normal rhythm of the heart is usually called the sinus rhythm. When the proper sequence or path of electrical signals is delayed or interrupted, an arrhythmia may develop. Anatomically, arrhythmias may be grouped according to the location where the disturbance in the electrical system arises, such as “ventricular” arrhythmias that arise in ventricles, and “atrial” or “supraventricular” arrhythmias that arise in heart tissue located above the ventricles.
In addition, arrhythmias are identified based on whether the electrical system malfunction is in the conduction of the electrical signal or impulse, or in the generation of the electrical signal or impulse. An impulse conduction failure will sometimes involve a phenomenon known as “re-entry,” which occurs when the electrical signal travels in closed pathway or loop. This can occur, for example, when the AV node fails to conduct the signal properly from the atria to the ventricles, and the resultant AV nodal re-entry can cause very rapid beating of atria, sometimes called “supraventricular tachycardia.” “Tachycardia” simply refers to a faster than normal heart rhythm.
One well known type of cardiac arrhythmia is known as atrial fibrillation. Atrial fibrillation, or AF, occurs when rapidly circulating abnormal electrical impulses stimulate the atrium to beat very fast—up to several hundred beats per minute or more. The rapid electrical pulses may also be passed by the AV node to the ventricles, causing fast and irregular ventricular contractions.
An increasingly well accepted procedure for treating cardiac arrhythmias in general, and atrial fibrillation in particular, is referred to as ablation. After the source of the disruption in the electrical system is determined, the tissue of the heart is ablated to eliminate the source of the aberrant impulses or to form a lesion or scar which interrupts and isolates the source of the aberrant electrical signal. It has been proposed to carry out such ablation by cryogenic probes or electrical radiofrequency (rf) energy electrodes. U.S. Pat. No. 6,161,543, for example, discloses various shapes of cryogenic probes that may be used to carry out the so-called MAZE procedure in which a series of lesions are formed strategically around the pulmonary trunk and elsewhere in the heart muscle to create an electrical maze that delays the aberrant electrical signals and prevents fibrillation of the atrium. U.S. Pat. No. 6,161,543 is incorporated by reference into this application, in its entirety.
Although cryosurgical probes and rf energy electrodes are used with increasing frequency in treating cardiac arrhythmias via heart tissue ablation, there continues to be a desire for additional apparatus and methods in the armamentarium of cardiologist for the detection and treatment of cardiac arrhythmia. For example, forming continuous linear lesions without breaks or disruptions and of uniform depth along the entire lesion lengths are challenging at the very least for cardiologists and electrophysiologists. Additionally, determination of the site of electrical malfunction requires what is known as electrophysiology mapping—which is commonly carried out as a separate procedure. It would be advantageous if the mapping and ablation could be carried out with the same instrument in the same procedure.
There also continues to be a desire for additional apparatus and methods in the armamentarium of cardiologist for the treatment or prevention of conditions resulting from the treatment of cardiac arrhythmias. For example, it is known that ablation around the pulmonary vein will sometimes result in stenosis, or closure, of the vein. Despite efforts to open the pulmonary vein and to place a stent in the vein to hold it open, patients suffering from repeated restenosis of the pulmonary vein often have a doubtful prognosis. Accordingly, there is a need to provide method and apparatus for alleviating stenosis of the pulmonary and other veins, that may be caused by other ablation treatment of cardiac arrhythmias.